The present invention relates, in general, to semiconductor processing methods, and more particularly, to process techniques for silicon carbide semiconductors.
In the past, the semiconductor industry has utilized a variety of techniques for etching silicon carbide semiconductor material. Typically, a layer of aluminum is used as a mask during the etching of silicon carbide. The aluminum is formed on the silicon carbide and patterned to expose areas of the silicon carbide that are to be etched. The exposed silicon carbide is then exposed to a nitrogen fluoride and oxygen (NF.sub.3 /O.sub.2) plasma to perform the etching. One problem is that the plasma sputters aluminum from the mask onto the substrate. The aluminum sputtered onto the substrate prevents uniform etching of the underlying silicon carbide, and can form a residue that prevents forming contacts to the silicon carbide.
Additionally, trenches formed by the plasma chemistry have substantially square corners. When the plasma chemistry is used to create mesa's for transistors, the square corners result in high electric fields at the corners which reduces the breakdown voltage of the transistor.
Accordingly, it is desirable to have a mask for etching silicon carbide that does not sputter material from the mask onto the silicon carbide during the etching process, and an etch chemistry that results in round corners.